What is the lower shoreface?
Jebbe van der Werf
The lower shoreface forms the transition between the inner shelf and upper shoreface (see Fig. 1). Lower shoreface sand transport is controlled by the combined action of waves and currents. The lower shoreface is covered by multiple types of bedforms ranging from small-scale ripples (a few decimeters long), tidal sand waves (100-1000 m long) to shoreface-connected ridges (5-10 km long).
Figure 1: Bathymetric chart of part of the Netherlands coastal zone, showing the lower shoreface and a variety of rhythmic bedforms including tidal sand waves. Data from Rijkswaterstaat & Netherlands Hydrographic Service.
Knowledge of lower shoreface sand transport and seabed morphodynamics (in particular of sand waves) is essential, as the lower shoreface controls to a large degree how offshore seabed activities and climate change affect nearshore functions such as coastal safety (see Fig. 2). This concerns the effect of sea level rise (SLR) on coastal evolution, as well as the impact of offshore wind farms, sand extraction and other human interferences. The lower shoreface is, in many cases, the sediment source for the upper shoreface and beach, and also mediates onshore wave energy transfer (Anthony & Aagaard, 2020). However, the lower shoreface bed dynamics are complex and poorly understood.
Figure 2: Three interrelated key aspects of lower shoreface bed dynamics addressed in MELODY. For adequate and sustainable marine & coastal management, we must understand both sand transport processes and the dynamics of tidal sand waves.
References:
Anthony, E.J., Aagaard, T., (2020). The lower shoreface: morphodynamics and sediment connectivity with the upper shoreface and beach. Earth-Science Reviews, 210, 103334. https://doi.org/10.1016/j.earscirev.2020.103334
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